Sunday, November 27, 2011

If you are planning to experiment with any Android phone/tablet, the first thing you would like to do is take a backup of it just in case things get messy. Typically in such situations you would like to take a backup of not only the user-data but also the operating system.

In this post I will be discussing on how to create a backup and restore the backup. You don't need to root your device for this since adb already has root access in HCL Me X1. But you will need fastboot which can be obtained by compiling the Android source code.

Remember that the source code can be built only on a Linux distribution, so make sure you have one (I would recommend Ubuntu 11.10). fastboot will be available at <source_code_dir>/out/host/linux-x86/bin/fastboot after the compilation. If you don't want to compile the source, you can try a compiled version of fastboot from the link specified at the end of the post; I built it on Ubuntu 11.10.

Replacing the Recovery Image

Before replacing the recovery image, create a backup of it in case you want to revert it back. Open the shell of the device using adb shell. Find the mount-point of the recovery image using cat /proc/mtd. There will be an entry like - mtd6: 00a00000 00200000 "recovery"

The recovery image can be created by reading the contents of the recovery mount-point and writing it into a file. This can be done using the following command - cat /dev/mtd/mtd6 > /sdcard/recovery.img

The recovery image is written to the sdcard in this case, you can redirect it anywhere you want to. The recovery image can be flashed back using fastboot. For this you have to boot the device into the bootloader using adb reboot-bootloader. The image can be flashed using the following command - fastboot flash recovery recovery.img

You can backup other mount points like system, userdata, etc. using this method but it's a lot easier to do so using the ClockworkMod's Recovery Image. You can download it from the link specified at the end of the post. Flash it using the same fastboot command as above.

Creating a Backup

Reboot the device into the ClockworkMod's recovery mode using adb reboot recovery. This console has options to backup and restore the operating system. However it does this using the sdcard, so make sure you have one in the device before you proceed.

From the recovery console, select Backup and Restore > Backup. After a series of messages the ROM will be backed up.

Restoring a Backup

From the recovery console, select Backup and Restore > Restore. Select the backup you want to restore. After a series of messages the ROM will be restored.

In case you are looking for the stock ROM you can find it here. It's not the exact stock ROM but an unrooted factory reseted ROM. And the original recovery image, ClockworkMod's recovery image and the compiled version of fastboot is available here.

Saturday, November 19, 2011

Android is primarily an operating system based on the Linux kernel. So similar to other Linux based operating systems Android has a special user account known as the root or super-user. Unlike other user accounts which have limited control over the operating system this account has complete access to the system.

However several (almost every) carriers and manufacturers don't allow users to access this account mainly due to security concerns. Few carriers and manufacturers also do this because they don't want users to access features for free when they can sell them :). Rooting is a process that allows users of phones/tablets to gain this privileged control (the root access). Here is an article with the Top 10 Reasons To Root Your Android Phone.

The process of rooting a device changes from device to device. It usually involves using an exploit to either gain temporary root access or to flash a custom recovery image to attain permanent root access. There are popular exploits like GingerBreak, psneuter, etc. and applications like GingerBreak.apk, SuperOneClick, etc. for rooting a device.

If you have read the articles and still want to go ahead let me remind you once again that trying to root your device might brick the device. I am not responsible if you brick your device, so proceed at your own risk.

Rooting the Device

You don't require any exploit or any application to root HCL Me X1 and in-fact vulnerabilities like GingerBreak have already been patched. However it is possible to root the device using the adb shell so make sure you have the Android Debug Bridge (ADB) on your system.

Connect the device through the USB and open the shell using adb shell at the command prompt. If you are seeing the # here then that indicates that your adb shell has root access. Instead if you are seeing a $ this process won't work for your device. Please put in a comment if you see $ so that me and the other readers know that HCL has changed something.

Typically in most of the devices the adb shell does not have root access. However, looks like the Android build of Me X1 isn't a production build. Not sure if this was done knowingly or unknowingly by HCL but either way the tablet has root access through the adb shell. You can confirm this by trying one of these -

Type adb root at the command prompt, it will show you a message stating that adbd is already running as root

Type getprop ro.secure at the adb shell, it shows 0

The ro.secure property can also be examined from the /default.prop. If this is 0 then it indicates that the adb will login as root by default. Note that this file cannot be changed since it's a part of the ramdisk

Though the adb shell has root access, the su command which is used in Linux doesn't work in Android since there is no su binary in Android. Download the su binary and the Superuser application from here (backup).

There are two steps for rooting the device -

Copying the su binary to the /system/bin directory

Since this directory is on the Android PATH, applications will be able to call su directly. However since the /system is a read-only file system (type mount at the adb shell to check this), the file cannot be directly copied. Push the su binary from the system/bin directory in the zip to a temporary folder of the device (like /data/local/tmp) using adb push. However note that the su binary does not work directly from this directory since applications on the /data file system do not have the setuid bit on. Remount the /system with read-write capabilities with the mount -o remount -rw -t yaffs2 /dev/block/mtdblock2 /system command (check the actual device mount-point using mount). Copy the su binary to /system/bin and set the permissions of the binary using chmod 4777 su.

Install the Superuser.apk from the system/app directory of the zip

Install the application using adb install or transfer the file to the sdcard and install it from there. The Superuser application intercepts the calls made to the su binary and informs the user about the usage so that unauthorized applications cannot attain root access.

Unrooting the Device

To unroot the device, uninstall the Superuser.apk and delete the su binary from the /system/bin directory.

Friday, November 04, 2011

As most of you know, Android is a mobile operating system initially developed by Android Inc. and presently being developed by the Open Handset Alliance led by Google. Android consists of a modified Linux kernel and software built on the Apache Harmony framework (an open source Java implementation). The best thing I like about the Android platform is its versioning. The code names are released in alphabetic order of dessert items - Cupcake, Donut, Éclair, Froyo, Gingerbread, Ice Cream Sandwich and Jelly Bean.

I am a newbie myself when it comes to Android, so the past few days I was trying to understand the various development models of Android. During my search I came across several good tutorials. This blog post is primarily to consolidate these tutorials for beginners like me.

Android, like most open source Operating Systems allows developers to look at development from two different perspectives - working on Android (Application development) and working with Android (Operating System development, not possible with proprietary Operating Systems). Google understands this and therefore has two different sites for Android developers - Android Developers (has the Android SDK to build applications) and Android Open Source Project (has the Android source code).

Android Developers

The Android Developers site provides various Development Kits to create applications for the Android platform. The Android SDK allows developers to write applications for the Android platform in a slightly modified version of Java which runs on a virtual machine called Dalvik.

The Android SDK can be installed by following the instructions specified here - Installing the SDK. And in case you want to start programming right away, here's a classic Hello World tutorial.

The Java APIs are pretty much what most developers use. However there might be situations where you would like to harness the true potential of the underlying Linux kernel through a low level language like C. Android does allow developers to do that but they cannot call the C binary directly as an application, they will need to go through Java with the JNI (Java Native Interface). This methodology of development is supported by the NDK (Native Development Kit).

The Android NDK can be installed by following the instructions specified here - Installing the NDK. The NDK does come with the Hello World example but it isn't as easy as the regular one.

The most useful tool Android provides developers with is the Android Debug Bridge. It is a command line utility that supports several commands like pulling/pushing files to and fro the device, installing applications, etc. This is one tool that every Android developer will have to use irrespective of whether he is developing applications or playing with the source code. Please note that the adb is part of "Platform Tools" which can be installed through the Android SDK Manager. If you stuck trying to install adb, read this.

Android Open Source Project

The Android Open Source Project site provides access to the source code of Android. A majority of the operating system infrastructure of Android is distributed under the Apache License and the core kernel is licensed under the GPLv2 License.

Certain developers use the Android Open Source Project to find vulnerabilities in the Android operating system and exploit them to execute tasks which cannot be done normally like attaining root access. Examples of these exploits are GingerBreak, psneuter, etc. Typically these vulnerabilities are patched for security reasons.

A majority of developers use the Android Open Source Project to modify and customize the operating system to create custom images. Several vendors add device drivers for their hardware and install pre-release applications to the operating system before flashing it onto the device. There have also been situations wherein vendors have customized the UI to suit their product lines before flashing.

You can obtain the complete source of the Android operating system by Downloading the Source Tree. There is an awesome tutorial on building Android 2.3.7 on Ubuntu 11.10 (64 bit) here. Even though the AOSP site specifies instructions on compiling the code, they are a bit outdated so visit the above link if you are stuck anywhere.

Underneath the layers of application frameworks, Android is primarily a Linux kernel and therefore is built on a C library. Unlike the traditional Linux based operating systems, Android uses a custom tiny libc called bionic. C programs can be written in an Linux environment running on x86/x64 architectures and cross compiled to Android running on ARM by linking Bionic to gcc. Here is an excellent tutorial which shows you exactly that. The compiled code can be run using adb shell. However note that codes compiled this way aren't recommended to be used with Java applications, the NDK should be used instead.

About Me

I have done my Engineering from Osmania University and am currently working as a Senior Software Developer at McGraw-Hill Financials. I previously worked as a Technical Evangelist (Campus Ambassador) at Sun Microsystems while I was doing my Engineering.